1. Field of the Invention
This invention relates in general to impact tools and in particular to an improved motorized impact tool using a spring and cam to cause reciprocating impacts.
2. Description of the Prior Art
Cam and spring powered impact tools concerned herein are used to deliver powerful reciprocating blows for heavy duty use, such as breaking up very hard formations like rock and concrete. This type of tool is not capable of being held by hand, but is normally mounted to a vehicle, such as a tractor, because of the large amount of energy delivered.
These impact tools have a motor for rotating an annular cam and roller assembly, which translates rotary motion to reciprocating motion. A hammer is connected to the cam and roller assembly for reciprocation, and a large coil spring provides the impact. A working tool is carried slidingly in the housing of the impact tool to transmit the energy from the hammer to the workpiece.
Should the working tool break through the workpiece, or should it not be in solid contact with the workpiece when the blow is delivered, then the energy from the hammer must be dissipated within the tool. Unless there are some means for absorbing the energy, the components will crack and break because of the large impact received.
In the patented prior art, rubber buffers are shown for absorbing blows when the energy cannot be transmitted fully to the workpiece. U.S. Pat. No. 3,179,185 shows a rubber attenuating means for a hand operated impact tool. Hand operated impact tools normally deliver 35-70 foot pounds of energy, while the impact tools of this invention deliver approximately 400 foot pounds of energy. If the energy cannot be transmitted to the workpiece, it must be absorbed by the tool and dissipated through heat from friction. While a rubber buffer may be satisfactory to absorb 35-70 foot pounds of energy, it would be completely unsatisfactory to absorb 400 foot pounds of energy because of the high temperatures generated. Local temperatures resulting from friction to absorb that amount of energy may be as high as 500.degree. to 600.degree. F. Such high temperatures would quickly cause deterioration of any rubber attenuating means.
A spring steel end stop, used with an explosive-driven apparatus for anchoring bolts, nails, and the like is shown in U.S. Pat. No. 3,566,978. In that device, the hammer wedges into a tapered bore in the end stop, expanding the end stop and absorbing a portion of the energy through friction and heat. Other springs cooperate with the expanding end stop to absorb the remainder of the energy. While such an energy absorbing device may be suitable for an explosive-driven impact tool, it is desired to have a less complex arrangement for the motorized impact tool of this invention.